The present paper's objective was to synthesize and characterize both the oxalic niobium precursor (NH 4 ) 3 NbO(C 2 O 4 ) 3 .H 2 O, and the product of its doping with Cu and calcining, CuNb 2 O 6 . In order to obtain the niobium precursor, commercially available niobium oxide (Nb 2 O 5 ) was subject to fusion with potassium bisulfate (KHSO 4 ). Once leached with water, the powder was complexed with oxalic acid and ammonium oxalate. The as produced material was manually mixed with copper nitrate Cu(NO 3 ) 2 .2H 2 O (25% Cu molar) and calcined at 1000°C in a muffle furnace. CuNb 2 O 6 was then obtained. The precursor was characterized by XRD, SEM, FT-IR, XRF, TG/DTG. The calcination product was characterized by XRD, XRF and SEM. Results show that single phase CuNb 2 O 6 could be obtained by this method without Nb 2 O 5 contamination.

Mechanical alloying (MA) can be highlighted among the various methods and powder processing forms, which consists of producing homogeneous materials from elementary powders. This process is of paramount importance as it has the ability to reduce the particle size of the powders and can often promote bonding between elements which have low interaction and wettability. This method is usually used in the route of powder metallurgy, and generally improves the sinterability and mechanical properties of the materials. In this context, the objective of this work was to analyze the evolution of mixtures of Al 2 O 3-5wt%-Ni and Al 2 O 3-5wt%-Nb powders submitted to the mechanical alloying process in a planetary ball mill for up to 40h. The morphological evolution was observed through Scanning Electron Microscopy (Field Emission Gun, SEM-FEG), energy dispersive spectrometry (EDAX) phases and particle sizes by Particulometry. It was observed that a significant micro structural change occurred in both compositions, indicating the formation of composite powders. This behavior was more intensely observed with the increase in the grinding time, obtaining composite powders with a more homogeneous and uniform structure with the time of 40 hours of MA.

The objective of this work is obtaining W-30 wt% Cu composite powder from ammonium paratungstate hydrated (APT) and hydrated copper nitrate and investigating the influence of some production process parameters of W-30 wt% Cu in particles form which results in high sinterability and densification of W-30 wt% Cu composite. To achieve this objective, the powder was obtained by manually mixing the APT and copper nitrate and reducing under a hydrogen atmosphere at 800 °C and then compacting at 500 MPa and sintering in a tubular furnace at 1200 °C for 60 minutes. The obtained materials were characterized by XRD, SEM, EDS, particle size analysis, density and microhardness measurements. The composite powder showed a good homogenization of Cu in W with very fine and agglomerated particles and a mean crystallite size of 25.64 nm. SEM coupled with EDS with mapping analysis revealed a homogeneous distribution of Cu and W in the sintered sample. The composite had a relative density of 96.77% and a microhardness of 523.66 HV. Therefore the method of obtaining the composite powder is feasible to sinter W-30 wt% Cu powder due to a greater dispersion and homogenization of phases and the average particle size.

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The use of niobium containing materials' has gained much attention of the scientific community in the late years due its various applications in diverse fields. NbC is a highly versatile material. Copper addition may alter several of its properties, such as morphology, crystal structure etc. as well as enhance its catalytic behavior. Nanostructured NbC with copper addition synthesis' presented here had the precursor [(NH 4 ) 3 [NbO(C 2 O 4 ) 3 ] x H 2 O] as starting material, which was doped with Cu(NO 3 ) 2 at 5% and 10% (molar) ratios. Doped NbC was obtained via gas solid reaction in fixed bed reactor at lower temperature (980°C) and with shorter reaction time (2h) than traditional methods. Reaction products' were characterized by XRD, crystal sizes were estimated according to HWL method, and SEM, XRF, BET and laser particle size analysis were performed. XRD indicated the formation of NbC and Cu phases with cubic crystal structure of ~20nm. SEM showed slight morphological change upon increasing copper content, indicating a less porous structure, which is consistent with BET data (43.7m2 /g for 5%Cu-NbC and 37m 2 /g for the 10% Cu-NbC). Crystal size calculations showed that increasing dopant content particle sizes were also increased, probably due to the presence of the dopant, in some extent, in the crystal structure.

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Resumo A pesquisa e o desenvolvimento de Materiais nanoestruturados vêm crescendo significativamente nos últimos anos. Estes materiais apresentam propriedades significativamente modificadas em comparação às dos materiais convencionais, devido às dimensões extremamente reduzidas dos cristalitos. O carbeto de Tântalo (TaC) é um material extremamente duro, apresentando elevada dureza, elevado ponto de fusão, elevada estabilidade química, boa resistência ao ataque químico e choque térmico e excelente resistência à oxidação e corrosão. Desta forma este trabalho teve como objetivo a obtenção de TaC nanoestruturado a partir do precursor tris(oxalato)oxitantalato de amônio hidratado, através de reação gás-sólido a baixa temperatura (1.000°C) e curto tempo de reação. Os materiais obtidos foram caracterizados através de difração de Raios-X (DRX), Refinamento Rietveld, Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Infravermelho (espectroscopia IV), Termogravimétrica (TG). Através das analises de DRX e do refinamento Reitiveld para o TaC com S = 1,1584 observou-se a formação do carbeto de tântalo puro com estrutura cúbica e tamanho médio de cristalitos na ordem de 12,5 nanômetros. Palavras-chave: Carbeto tântalo nanoestruturado; Precursores oxálicos; Reação gás sólido.